1. Field of Invention
The present invention relates to a method for receiving multi-cast packets, and more particularly to a method for receiving the multi-cast packets in which a retransmission request can be transmitted to a transmitting end.
2. Related Art
Multi-cast is a network technology that permits a multi-cast source to transmit a single packet to a plurality of receivers at the same time. Multi-cast can implement efficient data transmission from a single point to multiple points, so as to save network frequency bandwidth and reduce network load. Therefore, the multi-cast technology is often used in a large-scale data distribution system such as an image file downloading required by computer manufacturers.
The multi-cast technology generally uses user datagram protocol (UDP), but UDP does not perform flow control or error control, so UDP is an unreliable communications protocol. During the process of using the multi-cast technology for large-scale network data transmission, due to influences of factors such as a malfunction of network devices and network overload, as well as an unreliable transmission manner of the multi-cast technology, network packet loss is inevitable. Especially, when network congestion occurs, packet disorder or packet loss might easily occur.
Moreover, the multi-cast technology can support a maximum 64 Kilobyte (KB) packet, so during transmission of large-scale data blocks, the data block needs to be split into a plurality of packets to be transmitted. A receiving end receives the packets and then assembles the packets. During the transmission process, any packet loss causes incompleteness of the data block. In the conventional method, the incomplete data blocks (that is, a received part of the packets) are discarded, and retransmission is then requested. However, in this manner, a data amount transmitted on the network increases and the network load increases, and network congestion further results in a problem of a seriously low transmission success rate.